Impact absorption structure

ABSTRACT

The present invention includes an article of manufacture with a layer with a plurality of corrugations to form an energy absorbing structure, where each corrugation has a floor and two walls connecting the floor to the base layer and the length of each corrugation is longer than the widest width of the corrugation. The present invention also includes an energy absorbing structure with a multi-layer energy absorber having a layer with a plurality of surface features and a second layer with a second plurality of surface features wherein the surface features of one layer are nested within the surface features of the other layer such that the base layers are adjacent to each other. The present invention also includes a single step method of manufacturing the energy absorbers including forming a two layer material in a single step. Further, the present invention includes a method of absorbing impact energy that involves generating heat through friction between surface features on a pair of base layers.

FIELD OF THE INVENTION

The present invention relates to structures, including methods of useand manufacture, that absorb energy upon impact.

BACKGROUND OF THE INVENTION

Many materials and structures have been utilized to absorb energy duringan impact. They range from fabrics and foams to plastics. Despite thesematerials and structures, there continues to be a need for structureswith improved energy absorbing characteristics that are cost efficientto manufacture.

Recent materials include a sheet of material with a plurality of conicalprotrusions emanating from one side of the sheet. For example, U.S. Pat.No. 6,247,745 shows a base with a plurality of protrusions defined onthe base where the walls of the protrusions at least partially compressduring energy absorption. While suitable in many applications, a costsaving in manufacture of these structures might be available if thenumber of steps to manufacture these materials could be reduced. Inparticular, these prior art products require a production process thatincludes formation of the base and then formation of the protrusionswithin the base. Furthermore, the manufacturing methods used to makeknown materials result in inconsistent energy absorbers. For example,the walls of a protrusion may vary in thickness depending on thelocation of the wall that is measured. Furthermore, the thickness of thewalls of one protrusion may vary from the thickness of the walls of anadjacent protrusion. Such unevenness leads to an energy absorber that isinconsistent in its ability to absorb an impact's energy. This causesuncertainty in the effectiveness of the energy absorber.

As weight of materials is always a concern in vehicle manufacturing,there continues to be a need for lightweight structures that havecomparable or improved ability, relative to existing structures, toabsorb energy while also being cost-effective to consistentlymanufacture.

SUMMARY OF THE INVENTION

The present invention includes an article of manufacture with a layercombined with a plurality of corrugations to form an energy absorber,where the article is extruded and each corrugation has a floor and atleast two walls connecting the floor to the layer and the length of eachcorrugation is longer than the widest width of the corrugation. Thepresent invention also includes an energy absorber with a multi-layerenergy absorber having a layer with a plurality of surface features andat least one additional layer with a plurality of surface featureswherein the surface features of at least one layer are nested within thesurface features of the other layer such that at least two of the layersare adjacent to each other. The present invention also includes methodsof manufacturing the energy absorber structures including extruding anenergy absorber in a single step and forming a two layer structure in aslittle as one step. Further, the present invention includes a method ofabsorbing impact energy that involves generating friction betweensurface features on at least a pair of layers.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1A-B show perspective and close up cross sectional views of acorrugated energy absorber.

FIGS. 2A-F show cross-sectional views of several suitable corrugationshapes.

FIGS. 3A-B show perspective and cross sectional views of an energyabsorber with a plurality of protrusions.

FIGS. 4A-E show cross-sectional views of several multi-layer energyabsorbers.

FIGS. 5A-B show cross-sectional views of a raw hinged energy absorberand a completed, hinged, multi-layer energy absorber.

DETAILED DESCRIPTION

The present invention is directed to an improved and alternativeapproach to reinforcing structures and particularly automotive vehiclestructures. The invention is predicated on the discovery of a newstructure, that optionally may be formed in one step, having surfacefeatures such as in the form of corrugations or protrusions, at least atwo-layer material in which the surface features of one layer are nestedwithin the surface features of at least one other layer, which in oneembodiment uses friction to help absorb energy. Methods of manufactureand of use of these materials are also part of the present invention.

The energy absorber that may be formed in one step to include a layerwith any of a plurality of various surface features and particularlyfeatures selected from corrugations and protrusions, which surfacefeatures optionally are integrally formed with the layer and adapted toprovide the layer with increased energy absorbing characteristics.

In a first embodiment, as seen in FIG. 1, an illustrative energyabsorber 10 may include a base portion 12 in which a plurality ofcorrugations 14 have been formed, giving the energy absorber 10 arepeating structure, which may be continuous over the length ofstructure or discontinuous, may have repeating units of the same ordifferent wave length, have repeating units of the same or differentwaveform, or combinations thereof.

For example, as shown in FIG. 1, each corrugation 14 has a floor 16 andtwo walls 18 connecting the floor 16 to the base portion 12. The floorand the walls may be linear, curvilinear, combinations thereof or asotherwise configured. The corrugations have at least one length Ldimension that measures the distance from one end of the corrugation tothe other end and at least one depth D dimension that measures thedistance from the base portion 12 to the floor 16. At least one basewidth W1 dimension that measures the distance between the two wallswhere the walls meet the base portion. As used herein, the floor widthW2 shall be a measure of the size of the floor. The wavelength wouldinclude, for example, the distance spanning from a location on a surfacefeature to a similar location on an adjacent surface feature, whenviewed in cross-section.

Typically, the length of the corrugation is longer than either of thewidths to form a trench or groove. The corrugations typically do nothave enclosed ends, but may have such. The thicknesses of the baseportion, walls, and/or floor may vary along the cross-section of thestructure and may be selected to maximize energy absorption of thecorrugations, each of which may be varied, individually or incombination, across the layer. For example, thicker walls may exhibitincreased energy absorption versus comparatively thinner walls. Further,the thickness of the floor may increase over the cross-section of thestructure to provide increase energy absorption. By way of example, thethicknesses might range from about 5 mm to about 40 mm. Preferably, thethickness of base portion, walls and/or floors of the structure aresubstantially constant along the length of the structure.

The corrugations typically run parallel to one another, although otherarrangements may also be suitable, such as corrugations radiating from acentral location or from several locations. Also, the parallelcorrugations that are parallel to the longest dimension of the energyabsorber are preferred, but not required, because of the ease and costeffectiveness of their formation, as discussed below. Put another way,the orientation of the corrugations can be designed to be lateral orlongitudinal with respect to the supporting structure of the device orvehicle (e.g. body-in-white).

The shape of each corrugation may be constant across the energyabsorber, although this is not required, where the shape is generallydefined by the relationship of D, W1 and W2 to each other. Forcorrugations where the floor and walls are linear and the floor isroughly parallel to the base portion, each corrugation has an angle ordraft that is defined by the ratio of base and floor widths to eachother. One illustrative situation is where the base width W1 and thefloor width W2 are the same. This gives a square waveform appearance tothe cross-section of the energy absorber. Where the base width W1 islonger than the floor width W2, the draft is positive and the draft isnegative in the opposite situation. Preferably, the draft is betweenabout −45° and about +45°.

Other corrugation shapes utilizing curvilinear floors, walls and baseportions may also be used such as corrugations shaped to the give theenergy absorber a sine waveform or other rippling or undulatingwaveform. Other suitable curvilinear shapes include closed loops wherethe walls of one corrugation touch or are attached to the walls of theadjacent corrugation or the two walls of the loop touch or are attachedto each other. Open loops where the walls of adjacent corrugations andwalls of the corrugation are spaced apart. Partially open loopcorrugations may be suitable where either adjacent walls touch/areattached or both corrugation walls touch/are attached. Combinations ofopen, partially open and closed loop corrugations may also be suitable.

Exemplary cross-sections of energy absorbers are shown respectively inFIGS. 1A-B and 2A-E, such that the pattern of corrugations may be asquare waveform (W1=W2)(FIGS. 1A-1B), a positive draft (W1>W2)(FIG. 2A),a negative draft (W1<W2) (FIG. 2B), a sinusoidal waveform(FIG. 2C), anopen loop shape (FIG. 2D)or a closed loop shape(FIG. 2E). Although shownas having a constant waveform, the corrugations may have waveforms inwhich the sizes and shapes of corrugations vary. For example, thepattern may include alternating corrugations of different heights,widths, drafts, or combinations thereof; a series of corrugations withincreasing and/or decreasing heights, widths, drafts, or combinationsthereof; a series of alternating of open loops and closed loops;mixtures of shapes such as negative draft corrugations alternating withpositive draft corrugations, combinations thereof or the like.Corrugation patterns other than the square waveform are preferredbecause these patterns offer increased impact absorption for thoseimpacts that are not normal to the plane of the energy absorber. Forexample, with positive draft corrugations, the angle of impact may bemore closely parallel to walls then for a square waveform. As seen inFIG. 2A, Arrow A shows the angle of impact that is substantiallyparallel to walls 20 in a positive draft corrugation.

The corrugations may be sized and shaped to provide at least one surfacethat is substantially smooth, flat or planar. This may be done foraesthetic reasons or improving the functionality of the energy absorber,such as increasing the energy absorbing characteristics of the structureor providing a surface on to which other components of the vehicle maybe attached e.g. decorative covering. With two surfaces that aresubstantially smooth, flat or planar, as seen in FIG. 2B, theinstallation of the energy absorber is eased because the structure maybe installed without respect to direction because both surfaces areequally functional for attaching to the vehicle or decorative coverings.

The energy absorber may also include one or securing devices such asflanges, brackets, fasteners, projections or other suitable structuresthat are adapted to help secure the energy absorber to the body in whiteof the vehicle or to another component of the vehicle, such as to aroof, a headliner, deck lid, body panel, floor panel or instrumentalpanel. The securing devices may include structures that are integrallyformed with the energy absorber combined with separate components.Furthermore, the one or more securing devices may be located amongst oras parts of the corrugations for example a first area of corrugationsmay be separated form a second area of corrugations by a smooth, flat orplanar portion useful securing the energy absorber. Also, a screw, snapfit fastener on other fastener may be place in one or more of the wall,base on floor of a corrugation.

Furthermore, adhesives may be used to help secure the energy absorbers.The adhesive may be any suitable adhesive for the intended application.It may be a water based adhesive, a solvent based adhesive or otherwise.It may be a single component adhesive or a multi-component adhesive(e.g., a two-component adhesive). The multi-component adhesive may usethe components simultaneously or sequentially. It may be air cured,moisture cured, heat cured, radiation cured (e.g., IR or UV), radiofrequency cured, solvent loss cured, or otherwise cured. It may be amelt flowable, a liquid, a film, a powder, a gel or otherwise. It may bea pressure sensitive, an RTV adhesive, a hot-melt adhesive. It may be astructural adhesive in certain applications. It should be recognizedthat the use of the term adhesive herein is not intended to forecloseprimers or other bonding agents from the scope of the present invention.

In another embodiment, the adhesive may be a cure-on-demand adhesive,requiring a separate operation to cause the adhesive to begin to cure.In one embodiment this is achieved by using an encapsulated curing agentwhich is ruptured during assembly. In another embodiment this isachieved by removing a protective coating to expose the adhesive toambient conditions. Cure can be initiated by exposing the adhesive toheat, infrared or ultraviolet light sources, or to shearing forces andthe like. Additionally, the adhesive may be initiated by an organoboraneamine complex, such as those mention in U.S. 20020058764, which isincorporated by reference. Of course, it is always possible to employ anadhesive that does not have cure on demand capability.

An adhesive selected from any suitable adhesive family may be employedsuch as polyesters, polyamides, polyurethanes, polyolefins, epoxies,ethylene vinyl acetates, urethanes, acrylics, silanes, thioethers,fluorosilicones, fluorocarbons, combinations thereof or the like. Theadhesive may be a high temperature epoxy resin, a polyimide, a hybridpolyimide/epoxy resin adhesive, an epoxy novolac/nitrile rubberadhesive, a polythioether epoxy, combinations thereof or the like.

The energy absorbers of the present invention may be installed withoutrespect to the expected direction of impact. Typically, the materialwill be installed so that the floors of the surface features areadjacent to the vehicle component that is to be padded with the baseportion spaced apart from the vehicle component. But the oppositeinstallation may also be utilized, where the base portion is placeadjacent to the vehicle component. Also, the energy absorbers may beinstalled without regard to expected angle of impact. Preferably, theenergy absorber will be installed such that the expected angle of impactis normal to the plane of the energy absorber, but this is notnecessarily the case. In fact, the energy absorber may be installed suchthat the expected angle of impact is parallel to the plane of the energyabsorber or at angle in between normal and parallel to the plane of theenergy absorber. Indeed, often the expected angle of impact cannot bepredicted. In addition to installation at the time of manufacture of thevehicle, the energy absorbers may be installed aftermarket; for example,as part of an effort to remanufacture or repair the vehicle. Uponconclusion of the useful life of a vehicle, the present invention alsocontemplates steps of removing and recycling the structure.

In addition to the corrugations described above, surface features in theform of protrusions may also be utilized in multilayer energy absorbersdescribed below. Like a plurality of recesses, as seen in FIGS. 3A-3Beach recess 100 has a floor 102 and at least two walls 104 (when seen incross-section) connecting the floor 102 to the base portion 106. Thefloor and the walls may be linear, curvilinear, or combinations thereofwhen viewed in cross-section. Like corrugations, protrusions have alength L that measures the distance across and a depth D measuring thedistance from the base portion 106 to the floor 102. The base width W1is a measure of the distance between the two walls where the walls meetthe base portion. The floor width W2 is a measure of the size of thefloor. The protrusions are similar to the corrugations except that theprotrusions are typically self-contained in that they define a discretespace. The resulting energy absorber resembles a cupcake pan likestructure or an egg crate like structure.

In addition to the dimensional variation possible with corrugations,protrusions also have floor shape as another aspect of their shape thatcan be defined. For example, when viewed from above, as in FIG. 3A, itis apparent that the protrusions may have floor shapes that maybe round,oval, rectangular, other regular polygonal, irregular polygonal or otherregular or irregular shapes. Floor shapes that provide walls of theprotrusions with increased surface area are desired such as stars orX-shapes. Also, the floor shape of the protrusion need not be the sameas the shape of the protrusion where it meets the base portion or thefloor may be rotated compared to shape of the protrusion where it meetsthe base portion. Preferably, the length of the protrusion is similar toits width. The thicknesses of the base portion, walls, and/or floor maybe selected to maximize energy absorption of the protrusions.

The protrusions may by be arranged in any pattern on the base portion.For example, protrusions may vary is depth, floor shape, floorthickness, wall thickness, base portion thickness across the energyabsorber. Also, the protrusions may be arranged in rows, in concentriccircles or ovals, at the corners of triangles, rectangles, pentagons,hexagons or higher order regular or irregular polygons.

The layer preferably generally provides a planar energy absorber,although it may be adapted to provide a multitude of planes to theenergy absorber. Also, the layer may have regular or irregular shapesuch as those described with respect to the corrugations or protrusions,thus forming corrugations on corrugations or protrusions on protrusions,for example. Also, corrugations of one dimension may be interspersedbetween corrugations of another dimension. Likewise, protrusions ofvarying depth, for example, may be interspersed with each other. Inaddition, corrugations may be combined with protrusions on any layer.

The energy absorber may also include a substrate layer to which a layeris attached by adhesive, mechanical fasteners or welding, where thesubstrate layer is generally free of surface features and serves toincrease the dimensional strength of that layer or other purposes suchas improving the aesthetics of the energy absorber. The substrate mayalso be used to increase the frictional dissipation of energy by placingit in contact with the layer, as discussed below.

The energy absorber of the present invention may be made of any suitablematerial such as metals, ceramics or the like, but preferably they willbe made from plastics such as thermoplastics, thermosets, combinationsthereof or the like. The resultant material may be rubbery, flexible orrigid. The nature of materials selected for inclusion in the energyabsorber enables the manufacture of a structure with the desiredproperties. For example, homopolymers such as polypropylene (PP) orpolystyrene (PS) could be incorporated for rigid (e.g. “glassy”) energyabsorbers whereas impact modified thermoplastic polyolefin (TPO) or highimpact polystyrene (HI-PS) could be incorporated for ductile (e.g.“rubbery”) performance. Other examples of suitable materials includenylons, polycarbonates, polypropylenes, polyesters, polyurethanes,combinations thereof or the like. Co-polymers of the above mentioned orother polymers may also be suitable. The energy absorber could becomprised of a single layer of material (e.g. monolithic) or numerouslayers (e.g. co-extruded or laminated) of materials. A fiberreinforcement may be included (e.g. glass or carbon fiber) or thematerial may be filled, e.g. with mineral or glass filler.

The energy absorbers may be made using any conventional techniquesincluding extrusion, pultrusion, injection molding, blow molding,compression molding, thermoforming, or combinations thereof. The energyabsorbers with a lineal profile, e.g. corrugations, are preferredbecause with these surface features, the energy absorbers can be formedin essentially unlimited lengths, such as by extrusion or similarmethods. This permits a one step formation process, where previously twosteps were required, resulting in a cost savings associated withmanufacture.

Energy absorbers produced by extrusion and similar techniques are alsopreferred because they result in base, wall and/or floor thicknessesthat are substantially constant over the length of the energy absorber.Such an energy absorber consistently absorbs energy, no matter whichlocation on the energy absorber is tested. Furthermore, such consistencyof thickness is highly reproducible through the use of extrusion andsimilar methods, meaning that a given length of energy absorber may beindistinguishable from any other length of energy absorber. This levelof consistency drives down costs of manufacture because less is spent onwasted materials, less is spent on quality control and less is spent onproduction oversight.

In addition to the above benefits, extrusion and similar techniquespermit the creation of energy absorbers that are not possible throughthermoforming or molding techniques. In particular, energy absorberswith corrugations having negative draft, open loop and/or closed loopformations are not suitable for thermoforming or molding because suchshapes cannot be removed from the mold without causing significantdeformation, and thus damage, to the energy absorber.

In one example of the manufacture of the preferred energy absorber, anunlimited length of material may be pushed or pulled (both techniquesare termed extrusion herein) through a die to create the structure. Uponcuring and cutting to length, the energy absorber is ready forinstallation. The energy absorbers with corrugations could also beproduced in a one step process utilizing injection molding, blowmolding, sheet molding, or another process.

The energy absorbers with protrusions may also benefit from a one stepproduction process. For example, an energy absorber may be injection,blow or compression molded in one step.

A second embodiment of the present invention includes a multi-layerenergy absorber. As seen generally in FIG. 4, each multi-layer energyabsorber 200 includes at least two layers 202 and 204, each with surfacefeatures 206 and 208, with surface features of one layer being nestedwithin the surface feature of the other layer. In one aspect, themulti-layer energy absorber has differing structures, in that the firstsurface features differ from the second surface features in at least onestructural aspect, such as shape, depth, base width, floor width,average width, wall thickness, floor thickness, base thickness,combination thereof, or the like. In a second aspect, the multi-layerenergy absorber has differing compositional aspect, in that the materialof the first surface features differs from the material of the secondsurface features. In a third aspect, the multi-layer energy absorberutilizes friction to dissipate impact energy.

The first aspect of the multi-layer absorber with differing structuresis seen in cross-section in FIG. 4A. The first layer 202 has firstcorrugations 206 with walls 208 and the second layer 204 has secondcorrugations 208 with walls 210. As can be seen, second corrugations 208are nested within first corrugations 206. The nested corrugations havedepth dimensions that differ from each other, thus providing differingstructures and a space 212 between the floors 214 and 216 of the twolayers. Stated alternatively, the floors 214 and 216 are offset fromeach other, even though the layers 202 and 204 substantially remainadjacent to each other. In theory, the crush resistance of a materialwill typically be inversely proportional to the square of its depth(assuming constant wall thickness), meaning that the taller surfacefeature will buckle first, with the shorter feature buckling second,thus providing a two step energy absorbing feature for this embodiment.The space 212 is preferably filled with ambient air; however, it may befilled with another material such as foam, adhesive or other energyabsorber. Also, preferably, walls 210 and 208 are in contact with oneanother, although not necessarily. For example, the walls may beseparated by an adhesive or a material that raises the coefficient offriction of one or both of the walls, as discussed below.

In another aspect, the wall thicknesses may vary from one layer to theother. In theory, the crush resistance of a material will typically beproportional to the wall thickness, meaning that thicker walled surfacefeatures will buckle after (or at a higher load then) a thinner walledsurface features. This is another way of providing a two step energyabsorbing feature.

The second aspect of the multi-layer absorber with differing materialsis shown in cross-section in FIG. 4B. Here, the first layer 220 includescorrugations 242 (or protrusions) into which are nested the corrugations224 of the second layer 246 where the material of first corrugationsdiffers from the material of the second corrugations. In thisembodiment, the corrugations may be sized and shaped so that there is noappreciable space between the floors 228 and 230 of the twocorrugations. The materials of the corrugations differ in theircompositions and consequently their impact strength. In a preferredaspect, the first layer has a lower impact strength than the secondlayer. In a preferred embodiment, the differing materials of thecorrugation may be combined with surface features having differentstructures e.g. different wall thickness.

A combination of several aspects of multi-layer absorbers is shown inFIG. 4C. There, a first layer 240 with corrugations 242 havecorrugations 244 from a second layer 246 nested therein. The depths ofthe corrugations differ resulting in a space 248 between the floors ofthe corrugations. The thicknesses of the base layers, walls and floorsalso differ from each other. For example, the ratio of the thicknessesof the base layers may range from less than about 1:4 to more than 4:1.In addition, different materials where used for each layer. Thisparticular embodiment illustrates the use of two differing structuresand differing materials in a multi-layer absorber.

A third aspect of multi-layer energy absorber utilize formation of heatenergy to dissipate impact energy, e.g., such as by friction. Frictioncan arise from the contact of the surface features of the layers to eachother. Typically, the walls of the surface features will rub togetherduring impact. This rubbing provides a distinct and noticeableimprovement in the amount of energy absorbed by the multi-layerabsorber. For example, placing a friction destroying substance, e.g.lubricant, between nested surface features reduces the energy absorbingcharacteristics of the multi-layer absorber.

Any material that has a high coefficient of friction is desirable as asurface feature or layer material. Such high coefficient of frictionmaterials may have their coefficient of friction natively or as theresult from the manufacturing process and/or from post manufacturingprocessing. In addition, the high coefficient of friction may resultfrom the intentional formation of protrusions, valleys, micro ornano-textures or other features on the surface features. Theintentionally formed features are typically relatively small incomparison to the surface features. Also, the coefficient of friction ofthe surface features may be increased through the use of coatings orother surface treatments such as abrasives.

In one embodiment utilizing friction, the depths of the surface featuresmay be different, as discussed above, such that the floors are offsetfrom each other while the layers remain adjacent to each other (See FIG.4A). In another embodiment, the floors are offset from each other eventhough the depths of the surface features are about the same. In thisembodiment, the layers, too would be space from each other. For example,in FIG. 4D, a first layer 250 with corrugations 252 have corrugations254 from a second layer 256 nested therein. The depths of thecorrugations differ resulting in a space 258 between the floors of thecorrugations. Furthermore, there is a space 260 between the first andsecond layers. In a preferred embodiment, the distance between thelayers is greater than the distance between the floors. In thisembodiment, the amount of friction between the walls of the corrugationsis increased, thus increasing the amount of impact energy dissipated byenergy absorber. This embodiment may be of interest when the surfacefeatures are protrusions and the material is made by thermoforming. Withthis manufacturing technique, the protrusion may have a slight tomoderate mushroom shape that would prevent the protrusions of one layerfrom be able to fully nest within the protrusions of the other layer.

In another embodiment, positive draft surface features are combined withsquare wave surface features. As seen in FIG. 4E, a first layer 262 withsquare wave corrugations 264 have positive draft corrugations 266 from asecond layer 268 nested therein. The corners 270 of the square wavecorrugations 264 contact the walls 272 of the positive draftcorrugations 266 somewhere between the walls meet the base and thefloor. In this embodiment, the impact forces the positive draftcorrugations 266 into the smaller square wave corrugations 264, thushelping dissipate energy through friction. In a preferred embodiment, itis believed that if the comers 270 contact the walls 272 nearer thefloor, then more energy will be dissipated, whether by friction oranother mechanism. The depths of the corrugations may be adjusted toinsure that, during an impact, the floors of the two layers contact eachother before, after or when the bases of the two layers contact eachother.

In another embodiment, positive draft surface features are combined withnegative draft surface features. As seen in FIG. 5B, a first layer 274with negative draft corrugations 276 have positive draft corrugations278 from a second layer 280 nested therein.

One believed distinction between a two layer energy absorber and asingle layer energy absorber, whether the surface features are recessesor corrugations, is an increased ability to absorb impacts that are notnormal to the plane of the energy absorber. For example, comparing thesingle layer energy absorber in FIG. 2A with the two layer energyabsorber in FIG. 5B, shows that, with a given impact angle, as shownwith Arrow A, the two layer energy absorber has twice as many walls 282that are substantially parallel to impact direction than the singlelayer energy absorber, thus providing more impact absorption fornon-normal impacts. This is beneficial because, in real worldapplications, the angle of impact is rarely normal to the plane of theenergy absorber. In addition, some head impact scenarios result in acombination of translational and rotational energy dissipation where itis desired to absorb impact in each potential mode. Thus, the two layerenergy absorber would provide column buckling of a thermoplastic wall ina much wider range of potential impact directions as compared to asingle layer energy absorber.

Between two different two layer energy absorbers, there is believed tobe a benefit to spacing apart walls that are substantially parallel toone another. It is believed that energy absorbers with spaced apartwalls will more consistently absorb impact energy over a given area ofthe energy absorber than where the walls are adjacent to one another. Asseen in FIG. 5B, for example, the energy absorber has walls 282 that areparallel to one another but spaced from each other. On the other hand,as seen in FIG. 4D, the energy absorber has walls 284 that are parallelto one another but adjacent. Thus in the embodiment shown in FIG. 5B,the walls 282 are more evenly spread across an area of the energyabsorber compared to the embodiment in FIG. 4D, where the walls 284 aregrouped together.

While typically in the two layer energy absorber, the surface featuresof each layer have a common center line, this is not necessarily thecase. The center lines of the surface features may be shifted.

A preferred embodiment includes friction as an energy absorbingmechanism combined with buckling or elastic deformation. One example ofhow friction would be used to absorb energy is that the uppermost layermay be designed to buckle at a lower stress level than the lower layer.Upon buckling, the uppermost layer may then rub on or otherwise exertstress on the walls of lower layer. The lower layer may also be designedto buckle at some predetermined stress level.

The multi-layer absorbers may be made according to manufacturingtechniques discussed above or other known techniques. Preferredtechniques include those where both layers are formed in a single step(or on a single machine) such as co-extrusion or co-molding. Anothersingle step manufacturing technique for multi-layer absorbers isillustrated in FIG. 5. For example, a first portion 290 of the absorberis separated from a second portion 292 of the absorber by a hinge 294.The hinge 294 permits the first portion 290 to be folded on to thesecond portion 292, as indicated by Arrow B in FIG. 5A to arrive at themulti-layer energy absorber shown in FIG. 5B. As with other multi-layerabsorbers, one set of surface features nest into a second set of surfacefeatures. The hinge may be any device, feature or material the permitsthe movement of one portion of the energy absorber relative to the otherportion. The hinge is preferably one that is formed in the same processas the surface features such that the hinge is integral to the energyabsorber. For example, the hinge may be a valley, groove, otherdepression, thinning or other formation that imparts flexibility tomaterial of the energy absorber at that location. Other hinges may alsobe suitable such as after formed valleys or thinning of the material ofthe energy absorber. Likewise, the two portions of the energy absorbermay be manufactured and then attached via a hinge.

Other suitable manufacturing techniques include those where each layeris made in a single step (or their own machine) and then the layers arecombined to form the multi-layer absorber. Suitably, each layer may alsobe made with a multi-step process.

Materials for the multi-layer absorber may be selected from thosedescribed above with respect to the single layer energy absorbers. Inaddition, other components may be included to increase the energyabsorbing of the multi-layer absorber such as batting, foams, adhesivesand combinations thereof.

The layers of the multi-layer energy absorber may be attached to eachother through mechanical fasters, adhesives, welding or friction.Suitable adhesives include those discussed above. Welding may beaccomplished through the use of heat (e.g. spot welding) or through theuse some other electromagnetic energy (e.g. ultrasonic welding).

The present invention also includes methods of absorbing energy duringan impact. For example, energy may be absorbed by providing an energyabsorbing structures with corrugations and impacting the material withan object during a vehicle accident. Also, energy may be absorbed byproviding a two layer energy absorbing structure and dissipating impactenergy through friction. Dissipating impact energy may also beaccomplished by sequentially or simultaneously employing at least twodifferent structures or materials.

The materials of the present invention may be used in any type ofdevice, apparatus or structure that is in need of impact energyabsorbing characteristics. Preferred uses include in transportationvehicles such as fixed and rotary wing aircraft, spacecraft, buses,trains, subways, semi-trucks, pickup trucks, SUVs, and other passengervehicles. Within these vehicles the energy absorbing structurespreferably may be used in headliners, doors, bumpers, knee bolsters,seats, seat backs, floors, instrument panels and combinations thereof orthe like.

EXAMPLES

Computer aided engineering (CAE) was utilized to predict thecharacteristics of the present materials as compared to known materials.First, two layer energy absorber with differing depths of surfacefeatures (e.g. as shown in FIG. 4D) were compared to STRANDFOAM EA 1000,a known foamed energy absorber. The results are shown in Table 1, whereHIC is the “Head Injury Criterion”, the HIC(d) is a function of bothacceleration time history and the peak acceleration value, and theHIC(d)norm is normalized for thickness. TABLE 1 HIC Total HIC (d) NameDescription Thickness (d) norm Conical Structure 005 24 mm PS->19 mm PE25 mm 861 861 Conical Structure 105 24 mm PS->19 mm PE 25 mm 859 859Conical Structure 107 19 mm PE->24 mm PS 30 mm 948 1138 ConicalStructure 108 19 mm PE->24 mm PS 30 mm 922 1106 Strandfoam EA 1000Foamed material 25 mm 793 793

Thus, a double layer conical structure comprised of 24 mm PS sheet beingforced into a 19 mm PE sheet exhibits approximately 8% higher HIC(d)values than Strandfoam EA 1000, respectively. In addition, the data alsodemonstrates that forcing a weaker (e.g. taller) sheet into a stiffer(e.g. shorter) sheet improves normalized impact performanceapproximately 25% with the same weight.

In another series of experimental tests, the effect of friction wasinvestigated using CAE. Experimental tests on double layer conicalstructures with a 5 mm offset distance give the following results(utilizing structures such as seen in FIG. 3): TABLE 2 DescriptionComments Total Thickness HIC (d) 24 mm PS->24 mm PS Control 29 510 24 mmPS->24 mm PS Control 29 535 24 mm PS->24 mm PS Lubricated cones 29 55724 mm PS->24 mm PS Lubricated cones 29 583

Thus, the data demonstrates that the frictional dissipation provided bya 5 millimeter offset improves head impact protection by approximately10% versus similar samples with a lubricating agent.

The single layer corrugated portion of the invention utilizes simple—yetenergy absorbing efficient—geometrical features fabricated with low costraw materials and technologies, capable to match or improve the energyabsorbing performance of current art. The double layer portion of theinvention effectively utilized dual buckling and frictional dissipationenergy absorption mechanisms yielding improved efficiency against singlelayer current art solutions.

In other computer aided engineering simulations, 20 millimeter thickcorrugated and conical thermoplastic structures were impacted against anexperimental two-piece body-in-white (BIW) assembly with a 115millimeter length and a mean BIW HIC(d) value of approximately 1,500.Each structure was modeled using polypropylene impact copolymerthermoplastic resin (INSPIRE C702-20). Each simulation assumed thecorrugated structures are bonded to a 0.75 millimeter thick plate thatsimulated a headliner substrate. The data demonstrates an approximate14% and 17% improvement in the impact criterion for both negative andpositive draft corrugated part designs, respectively. Each of thesecomparisons is based upon a single layer vacuum thermoformed conicalstructure.

Thinning effects of the base layer or surface feature walls aretypically encountered in vacuum thermoforming manufacturing processes.In an effort to quantify such effects, measurements were taken invarious location of a single layer vacuum thermoformed conicalstructure. The conical structures were approximately 24 millimetersdeep. The wall thickness can vary as much as 40-50% from the base sheetthickness in a vacuum thermoforming process. Thus, in order to achievecomputer aided performance modeled with a 1.0-millimeter uniform wallthickness, a 1.6-millimeter base sheet thickness would be required forsingle layer conical vacuum thermoformed products. A part weightcomparison of corrugated and vacuum thermoformed conical energyabsorbing parts shows that, for comparable impact performance, a mere0.0065 kg mass increase is required for a single layer corrugated energyabsorbing structure versus a single layer vacuum thermoformed conicalparts.

Additional CAE simulations are performed on positive draft corrugatedenergy absorbing structures with varying draft angles. Each structure ismodeled with a 0.75-millimeter base thickness and a 1.75-millimeter wallthickness whereas the overall thickness is held constant at 20millimeters. The resultant data demonstrated that optimal performancecan be achieved with a positive draft angle of between about 0° andabout 10°.

Finally, a series of CAE simulations are performed on positive draftcorrugated structures with varying numbers (3<N<6) of corrugations. Eachstructure is modeled with a 0.75-millimeter base thickness, a1.75-millimeter wall thickness and a 9.2° draft angle. Each simulationis performed with a 115 millimeter length and a part width of100-millimeters. As the number of corrugations increases, the base width(11.5 mm<w<4.7 mm) of the corrugation decreases. Impact performance ofpositive draft corrugated part designs is measured as a function of thenumber of corrugations. The data demonstrates that sheet thicknessdecreases as the number of corrugations increases. Thus, part weightreduction could be achieved by increasing the number of corrugations ina given part design.

It will be further appreciated that functions or structures of aplurality of components or steps may be combined into a single componentor step, or the functions or structures of one step or component may besplit among plural steps or components. The present inventioncontemplates all of these combinations. Unless stated otherwise,dimensions and geometries of the various structures depicted herein arenot intended to be restrictive of the invention, and other dimensions orgeometries are possible. Plural structural components or steps can beprovided by a single integrated structure or step. Alternatively, asingle integrated structure or step might be divided into separateplural components or steps. In addition, while a feature of the presentinvention may have been described in the context of only one of theillustrated embodiments, such feature may be combined with one or moreother features of other embodiments, for any given application. It willalso be appreciated from the above that the fabrication of the uniquestructures herein and the operation thereof also constitute methods inaccordance with the present invention.

The explanations and illustrations presented herein are intended toacquaint others skilled in the art with the invention, its principles,and its practical application. Those skilled in the art may adapt andapply the invention in its numerous forms, as may be best suited to therequirements of a particular use. Accordingly, the specific embodimentsof the present invention as set forth are not intended as beingexhaustive or limiting of the invention. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but should instead be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. The disclosures of all articles and references,including patent applications and publications, are incorporated byreference for all purposes.

1-33. (canceled)
 34. An energy absorber structure comprising, a firstlayer having a first plurality of surface features and a second layerwith a second plurality of of surface features wherein the surfacefeatures of one layer are nested within the surface features of theother layer and the cross-sectional shape of the first layer surfacefeatures are different than the surface features of the second layer.35. The energy absorber structure of claim 34, wherein thecross-sectional shape is selected from the group consisting of squarewaveform, positive draft, negative draft, sinusoidal waveform, open loopshape, closed loop shape or combinations thereof.
 36. The energyabsorber structure of claim 35, wherein the cross-sectional shape of onelayer is negative draft and the other layer is positive draft.
 37. Theenergy absorber structure of claim 35, wherein at the first layer,second layer surface or both have friction raising attributes selectedfrom the group consisting of protrusions, valleys, micro textures, nanotextures, coating, abrasive or combinations thereof thereon.
 38. Theenergy absorber structure of claim 34, wherein the first and secondlayer are a plastic.
 39. The energy absorber structure of claim 38,wherein the first and second layer are different plastic compositions.40. The energy absorber structure of claim 39, wherein the first andsecond layer are attached by mechanical fastners, adhesives, welds,friction or combination thereof.
 41. The energy absorber structure ofclaim 40, wherein the first and second layer are attached by welds. 42.The energy absorber structure of claim 41, wherein the welds are spotwelds.
 43. The energy absorber structure of claim 35, wherein thecross-sectional shape of one layer is negative draft and the other layeris square draft.
 44. An energy absorber structure comprising, a firstlayer having a first plurality of surface features and a second layerwith a second plurality of of surface features wherein the surfacefeatures of one layer are nested within the surface features of theother layer and the first layer, second layer or both have frictionraising attributes selected from the group consisting of protrusions,valleys, micro textures, nano textures, coating, abrasive andcombinations thereof thereon.
 45. The energy absorber structure of claim44, wherein both the first and second layer have friction raisingattributes.
 46. The energy absorber structure of claim 44, where thefriction raising attributes are selected from the group consisting of ofprotrusions, valleys, micro textures, nano textures, and combinationsthereof thereon